MYISAM TABLE CAUSES THE SERVER TO CRASH

Issue:
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During index maintanence, R-tree node might need a split.
In some cases the square of mbr could be calculated to
infinite (as in this case) or to NaN. This is currently
not handled. This is specific to MyISAM.

SOLUTION:
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If the calculated value in "mbr_join_square" is infinite or
NaN, set it to max double value.

Initialization of output parameters of "pick_seeds" is
required if calculation is infinite (or negative infinite).

Similar to the fix made for INNODB as part of Bug#19533996.